1. Field of the Invention
The present invention relates to a method and an apparatus for generating images suitable for use with apparatuses utilizing computer graphics such as video game machines and graphic computers which must perform a high level of visualization using limited hardware resources.
2. Description of the Related Art
In video game machines and graphic computers, a drawing device portion is provided between the CPU and frame buffer (frame memory) in order to improve the processing speed. During the generation of an image, the CPU does not directly access the frame buffer, but generates commands to draw basic figures such as triangles and quadrangles and sends them to the drawing device portion. The drawing device portion interprets those commands from the CPU and draws the figures on the frame buffer.
The smallest unit a figure processed by the drawing device portion is referred to as a polygon or primitive and a command to draw it is referred to as a draw command or display list.
In a 3D (three-dimensional) graphics system in which an object is drawn on a two-dimensional display screen with a three-dimensional appearance, the surface of the 3D object to be rendered is divided into a plurality of polygons, and the polygons are sequentially drawn on a frame buffer to reconstruct an image having a three-dimensional appearance.
For example, when a 3D object OJ as shown at FIG. 6A is drawn, as shown at FIG. 6B, the surface of the object OJ is divided into a polygon Pa with vertices A, B, D, and C, a polygon Pb with vertices D, C, E, and F, and a polygon Pc with vertices B, C, G, and F. Then, as shown at FIG. 6C, draw commands IPa, IPb, and IPc associated with the polygons Pa, Pb, and Pc, respectively, are sequentially transferred to a drawing device portion 62 to sequentially draw the polygons Pa, Pb, and Pc on a frame buffer 66.
In the draw commands IPa, IPb, and IPc, the coordinates of the vertices of the respective polygons Pa, Pb, and Pc are added to respective indication codes INCO indicating that the subsequent data are polygon draw commands.
In applications such as video game machines, scenes frequently appear where 3D objects as described above are displayed by simply translating them. In such a case, the coordinates of the vertices of all of the polygons that form the object have been rewritten on a frame-by-frame basis.
Specifically, assume that the object OJ as shown at FIG. 6A is translated on the display screen in X and Y directions by amounts dx and dy, respectively. In the main memory, as shown in FIG. 7, the coordinate values of each of the vertices in the draw commands IPa, IPb, and IPc associated respectively with the polygons Pa, Pb, and Pc which constitute the object OJ are greater respectively by dx and dy in the frame Fb after the translation than in the frame Fa before the translation.
The applicant has made the following Japanese patent applications which are related to the drawing device according to this application.
05-190763 (filed on Jun. 30, 1993) corresponding to U.S. application Ser. No. 269,076, filed Jun. 30, 1994.
05-190764 (filed on Jul. 2, 1993) corresponding to U.S. application Ser. No. 267,678, filed Jun. 29, 1994.
05-258625 (filed on Oct. 15, 1993) corresponding to U.S. application Ser. No. 320,272, filed Oct. 11, 1994.
06-027405 (filed on Jan. 31, 1994) corresponding to U.S. application Ser. No. 369,745, filed Jan. 27, 1995.
Each of the above applications is owned by the assignee of the present invention.
When an object is translated on a display screen by rewriting the coordinates of the vertices of all of the polygons that constitute the object on a frame-by-frame basis as described above, the main memory must be frequently accessed, and this results in a problem in that the translation process can not be performed at high speed.